The present invention relates to an under trimming device for a multi-needle sewing machine with longitudinally extended looper, and more particularly to an under trimming device for a multi-needle sewing machine with multiple longitudinally extended loopers to simultaneously cut looper threads and needle threads respectively threading through different loopers and needles and make the cut threads have free ends with the same length. The under trimming device according to the present invention may effectively avoid the device from coming into collision with or interfering with the needles, loopers, and other accessories of the sewing machine, permitting the sewing machine to have stable thread cutting and simplified assembling.
A multi-needle sewing machine is widely used in the sewing industry. In which, multiple needles over a-needle plate of the sewing machine are used to guide multiple needle threads while multiple loopers below the needle plate, which have the same numbers and position corresponding to those of the multiple needles, are used to guide multiple looper threads. The needles and the loopers move alternately to complete the sewing, that is, the so-called chain sewing. Since the sewing principle and procedures are not the point of the present invention, they are not discussed herein.
The under trimming device of the present invention is used with a multi-needle sewing machine with multiple longitudinally extended loopers. In this type of sewing machine, a looper thereof sways back and forth in the sewing direction to guide the looper thread. The technical issue to be discussed in the present invention is: how to automatically cut the needle threads and the- looper threads at the time the sewing is completed with the cut needle threads and looper threads being positioned in place and having free ends with the same length so as to facilitate the next sewing.
Most of the conventional multi-needle sewing machines have an under trimming device which sways at an angle relative to the sewing direction so as to catch the needle threads and the looper threads and pull the same to a predetermined position to cut them off. Alternatively, a cutting device is disposed to the side of and in perpendicular to the sewing direction to reciprocate in one single direction so as to catch the needle threads and the looper threads and pull them to a predetermined position for cutting off. R.O.C. (Taiwan) Utility Model Patent Application No. 75208857 discloses an under trimming device for a multi-needle sewing machine, in which a driving means is used to drive a catcher of the under trimming device to travel at an angle relative to the sewing direction so as to hook, cut, and clamp the needle threads and the looper threads. R.O.C. (Taiwan) Patent Application No. 81107878 discloses a method of trimming threads of sewing machine and an under trimming device thereof, in which an under trimming device is disposed to one side of the sewing line to reciprocate diagonally and thereby hooks and cuts the needle threads and the looper threads.
The following disadvantages are found in the conventional under trimming devices for a multi-needle sewing machine:
1. The member used to catch or hook the needle threads and the looper threads sways in a curved track and thus easily comes into collision with the loopers and becomes damaged. PA1 2. To clamp free ends of the cut threads and hold the same in place, the member for catching the needle threads or the looper threads must not be disposed too far away from the needle plate of the sewing machine. Instead, the catch mender must be considerably close to the needle plate to ensure the clamping of threads. However, the close position of the catch member to the needle plate tends to interfere with the movement of the catch member while the distant position of the catch member from the needle plate tends to give too long free ends of the cut threads. PA1 3. An under trimming device either moving angularly or reciprocating laterally shall cause the cut threads to have free ends of different lengths which is obviously adverse to a successful start of the next sewing operation.
The above described disadvantages become more serious in a multi-needle sewing machine with longitudinally extended loopers. It is therefore tried by the inventor to develop an under trimming device for such sewing machine to eliminate the above disadvantages.